Solid state electrolyte cell having at least one electrode impregnated with a solid electrolyte

ABSTRACT

A solid electrolyte cell in which the state of electrical contact between the solid electrolyte and the layers of active materials of the positive and negative electrodes and the inter-particulate distance in the layers of active materials of the positive and negative electrodes can be optimized to assure superior load characteristics, and a method for manufacturing the cell. The method for manufacturing a solid electrolyte cell includes a step of applying a paint containing an active material and a binder to a current collector to form a layer of an active material, and a step of impregnating a solid electrolyte in the layer of the active material formed by the active material layer forming step. The impregnating step includes applying the paint comprised of the solid electrolyte dissolved in a solvent on the layer of the active material to allow the paint to be permeated into the layer of the active material, and subsequently drying the solvent.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a solid electrolyte cell in which asolid electrolyte is impregnated in a positive electrode active materialor in a negative electrode active material, and a method for producingthe cell.

[0003] 2. Description of the Related Art

[0004] Recently, many types of portable electronic equipments, such as avideo tape recorder with a built-in camera, portable telephone or aportable computer, have made their debut, and attempts are being madefor reducing their size and weight. Also, researches into cells asportable power sources of these electronic equipments, in particular thesecondary cells, are proceeding. Of lithium cells, among these secondarycells, researches and investigations into the thin type cell or foldablecells are proceeding most briskly. As the electrolytes for these cells,investigations into the solid electrolyte obtained on solidifying theelectrolyte, are proceeding energetically. In particular, high molecularsolid electrolyte having lithium salts dissolved in the high-molecularmaterial or the gelated solid electrolyte containing a plasticizer, arestirring up notice.

[0005] With the solid electrolyte, the cell can be reduced in thicknessmore significantly than with the liquid electrolyte, while there is norisk of leakage of the cell contents. However, if the solid electrolyteis used in a cell, it is not fluid as is the liquid electrolyte, so thatit can hardly be contacted in an ideal state with the electrode. Sinceions are migrated in the cell through the solid electrolyte or thegelated electrode, the contacting state between the solid electrolyteand the electrode affects the cell performance significantly. If thecontacting state between the solid electrolyte and the electrode ispoor, the contact resistance between the solid electrolyte and theelectrode is increased to increase the internal resistance of the cell.Moreover, ions cannot be migrated in an ideal state between the solidelectrolyte and the electrode to decrease the cell capacity. It istherefore crucial for the solid electrolyte to have a sufficiently tightcontact with a layer of the active material of the electrode.

[0006] It is reported in Japanese Laying-Open Patent H-2-40867 to use apositive electrode composite, obtained on adding a solid electrolyte tothe layer of the active material of the positive electrode to improvethe contact state between the solid electrolyte and the electrode. Inthe cell disclosed in this publication, a portion of the solidelectrolyte is mixed to a layer of the active material of the positiveelectrode to improve the state of electric contact between the solidelectrolyte and the electrode.

[0007] With the cell disclosed in this publication, since the positiveelectrode plate is fabricated using a positive electrode compositeadmixed with the solid electrolyte, and a solid electrolyte is layeredon the positive electrode plate, it is difficult to realize an idealcontact state between the positive electrode plate and the solidelectrolyte. In particular, if the solid electrolyte having a roughedsurface is layered on the electrode layer, the two are bonded only in apoor contact state to increase the internal resistance, thus worseningthe load characteristics.

[0008] Moreover, the positive electrode composite admixed with the solidelectrolyte, or the negative electrode composite, cannot be pressedsufficiently because of the elasticity proper to the solid electrolyteto increase the inter-particulate distance in the composite and hencethe internal resistance, thus again worsening the load characteristics.

[0009] In addition, the positive electrode composite admixed with thesolid electrolyte, or the negative electrode composite, need to befabricated at low humidity to prevent decomposition of the electrolyticsalt contained in the solid electrolyte. This not only raisesdifficulties in quality control but increases the cost significantly.

SUMMARY OF THE INVENTION

[0010] It is therefore an object of the present invention to provide asolid electrolyte cell in which the electrical contact state between thesolid electrolyte and the layers of the active materials of the positiveand negative electrodes and the inter-particulate distance in the layersof the active materials of the positive and negative electrodes can beoptimized to assure superior load characteristics, and a method forproducing the solid electrolyte cell.

[0011] In one aspect, the present invention provides a solid electrolytecell including an electrode having a current collector and a layer of anactive material formed on the current collector and containing an activematerial and a binder, in which a solid electrolyte layer is formed byimpregnating a solid electrolyte dissolved in a solvent on the layer ofthe active material.

[0012] In the solid electrolyte cell of the present invention, since thesolid electrolyte is impregnated in the layer of the active material,adhesion between the electrolyte and the active material is improved.

[0013] In another aspect, the present invention provides a method formanufacturing a solid electrolyte cell including the steps of applying apaint containing an active material and a binder to a current collectorto form a layer of an active material, and impregnating a solidelectrolyte in the layer of the active material formed by the activematerial layer forming step. The impregnating step includes applying thepaint comprised of the solid electrolyte dissolved in a solvent on thelayer of the active material to allow the paint to be permeated into thelayer of the active material and subsequently drying the solvent.

[0014] In the manufacturing method of the solid electrolyte cellaccording to the present invention, the paint containing the activematerial and the binder is coated on the current collector to form alayer of the active material during the active material layer formingstep. In the impregnating step, the paint comprised of the solidelectrolyte dissolved in the solvent is applied on the layer of theactive material to allow the paint to be permeated into the activematerial layer. The solvent is then dried to impregnate the solidelectrolyte in the active material layer. In the manufacturing method ofthe solid electrolyte cell according to the present invention, theadhesion between the solid electrolyte and the active material isimproved by impregnation of the solid electrolyte into the layer of theactive material.

[0015] Thus, the contacting performance between the active material andsthe electrolyte is improved to reduce the internal resistance to achievea cell having superior load characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a cross-sectional view showing an illustrative structureof a solid electrolyte cell according to the present invention.

[0017]FIG. 2 is a schematic perspective view showing only essentialportions of another illustrative structure of a solid electrolyte cellaccording to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] An illustrative structure of a solid electrolyte cell accordingto the present invention is shown in FIG. 1. The solid electrolyte cellincludes a positive electrode plate 1, comprised of a layer of an activematerial of the positive electrode 1 b and a solid electrolyte layer 1 cformed on a positive electrode collector 1 a, a negative electrode plate2, comprised of a layer of an active material of a negative electrode 2b and a solid electrolyte layer 2 c formed on a negative electrodecollector 2 a, and a separator 3 for separating the positive electrodeplate 1 from the negative electrode plate 2. The solid electrolyte cellalso includes a sheathing material 4 for holding the positive electrodeplate 1, a sheathing material 5 for holding the negative electrode plate5 and a hot melt material 6 for bonding the sheathing materials 4 and 5together.

[0019] The positive electrode plate 1 is comprised of a metal foil, suchas an aluminum foil, serving as a positive electrode collector 1 a, anda positive electrode mixture containing the active material for thepositive electrode and the binder coated thereon and dried in situ toform the layer of the active material of the positive electrode 1 b. Onthe layer of the active material of the positive electrode 1 b is alsoformed a solid electrolyte layer 1 c, as will be explained subsequently.

[0020] For the active material for the positive electrode, metal oxides,metal sulfides or specified high-molecular materials may be useddepending on the type of the cell under consideration.

[0021] For constructing a lithium ion cell, for example, metal sulfidesor oxides, such as TiS₂, MoS₂, NbSe₂ or V₂O₅ may be used as the activematerial for the positive electrode. Also, lithium compound oxides,formed mainly by Ll_(x)MO₂, where M denotes one or more transitionmetals and x is usually not less than 0.05 and not larger than 1.10depending on the charging/discharging state of the cell. As thetransition metals M making up the lithium compound oxides, Co, Ni or Mnis preferred. Specified examples of the lithium compound oxides includeLiCoO₂, LiNiO₂, LiNi_(y)CO_(1-y)O₂, where 0<y<1, and LiMn₂O₄. Theselithium compound oxides, capable of generating high voltage, can serveas an active material for the positive electrode having excellent energydensity. Plural sorts of the active materials for the positive electrodecan be used in combination as the positive electrode.

[0022] As a binder for the positive electrode mixture, any suitableknown binder may be used, while an electrically conductive agent or anysuitable known additive may be added to the positive electrode mixture.

[0023] As for the negative electrode plate 2, a negative electrodemixture containing the active material for the negative electrode andthe binder is coated on a metal foil, such as a copper foil, acting as anegative electrode collector 2 a, and is dried in situ to constitute alayer of an active material for the negative electrode 2 b. On the layerof an active material for the negative electrode 2 b is further formed asolid electrolyte layer 2 c, as will be explained subsequently.

[0024] For producing the lithium ion cell, it is preferred to use amaterial capable of doping/undoping lithium as the active material forthe negative electrode. Examples of the material capable ofdoping/undoping lithium include a carbonaceous material difficult tographatize and a graphite-based carbon material.

[0025] The above-mentioned carbonaceous materials may be enumerated bypyrolytic carbon, cokes, graphites, vitreous carbon fibers, firedorganic high-molecular compounds, carbon fibers and activated charcoal.The cokes may be enumerated by pitch coke, needle coke and petroleumcoke. The fired organic high-molecular compounds mean phenolic resins orfuran resins fired and carbonated at a suitable temperature.

[0026] In addition to the carbon materials, high-molecular materials,such as polyacetylene or polypyrrole, or oxides, such as SnO₂, may beused as the capable of doping/undoping lithium.

[0027] As a binder for the negative electrode mixture, theabove-mentioned negative electrode mixture admixed with known additivesmay be used in addition to known binders.

[0028] In the solid electrolyte cell of the present embodiment, a solidelectrolyte layer 1 c is formed on the layer of an active material ofthe positive electrode 1 b and a solid electrolyte layer 2 c is formedon the layer of an active material of the negative electrode 2 b. Thesesolid electrolyte layers 1 c, 2 c are formed by impregnating the activematerial of the positive electrode 1 b or the active material of thenegative electrode 2 b with a solid electrolyte. By impregnating layersof the active material with the solid electrolyte, the internalresistance of the cell is decreased, while the contact state between theactive material and the solid electrolyte layer is improved.

[0029] It is desirable for the solid electrolyte used in the solidelectrolyte cell of the present embodiment to contain a plasticizer andto be in a gelated state. By using the gelated solid electrolyte, it ispossible to improve the contact state between the electrolyte and theactive material and to render the cell flexible. In the followingexplanation, the gelated solid electrolyte containing the plasticizer istermed a gelated electrolyte.

[0030] For the plasticizer, esters, ethers or carbonic acid esters maybe used alone or as a component of the plasticizer. The content of theplasticizer is preferably not less than 10 wt % and not more than 80 wt% based on the content of the gelated electrolyte. If the plasticizercontent is larger than 80 wt %, mechanical strength cannot bemaintained, even if the ionic conductivity is that high. If the contentof the plasticizer is less than 10 wt %, ionic conductivity is low, evenif the mechanical strength is high. The content of the plasticizer ispreferably not less than 10 wt % and not more than 80 wt % based on thecontent of the gelated electrolyte for optimum tradeoff between theionic conductivity and the mechanical strength.

[0031] The plasticizer also contains lithium salts. As lithium saltsused in the gelated electrolyte according to the present invention,those used for the usual cell liquid electrolyte may be used. Examplesof the lithium salts include LiPF₆, LiBF₄, LiAsF₆, LiClO₄, LiCF₃FO₃,LiN(SO₂CF₃)₂, LiC(SO₂CF₃)₃, LiAlCl₄ and LiSiF₆. Of these, LiPF₆ andLiBF₄ are preferred for oxidation stability. Although the concentrationof lithium salts of not less than 0.1 mol/l and not larger than 3.0mol/l is acceptable, it is desirably not less than 0.5 mol/l and notlarger than 2.0 mol/l.

[0032] As the high-molecular matrix material used for gelating theabove-mentioned plasticizers, a variety of high-molecular materials usedin constructing the gelated electrolyte may be used. Specifically,fluorine-based high-molecular materials, such as polyvinylidene fluorideor a copolymer of polyvinylidene fluoride with hexafluoro propylene,etheric high-molecular materials, such as polyethylene oxide orcross-linked polyethylene oxide, methacrylate esteric high-molecularmaterials, acrylate high-molecular materials or polyacrylonitrile, maybe used alone or in a mixture. Of these, the fluorine-basedhigh-molecular materials are preferred since these improve stability inoxidation and reduction.

[0033] The high-molecular matrix material is preferably used in anamount of not more than 10 wt % and not less than 50 wt % based on theweight of the gelated electrolyte.

[0034] The solid electrolyte cell of the present invention is fabricatedas follows:

[0035] The positive electrode is prepared by evenly coating a positiveelectrode mixture containing the active material for the positiveelectrode and the binder on a metal foil, such as an Al foil,functioning as a positive electrode collector 1 a, and drying themixture in situ to form a layer of an active material of the positiveelectrode 1 b. As the binder for the positive electrode mixture, anysuitable known binder may be used, while any suitable known additive maybe added to the positive electrode mixture.

[0036] The solid electrolyte layer 1 c is formed on the layer of theactive material of the positive electrode 1 b to provide the positiveelectrode plate 1, while the solid electrolyte layer 2 c is formed onthe layer of an active material of the negative electrode 2 b to providethe negative electrode plate 2.

[0037] For preparing the solid electrolyte layers 1 c, 2 c, aplasticizer containing lithium salts and a high-molecular matrixmaterial are dissolved in a solvent to prepare an electrolyte solutionwhich is then uniformly coated on the layer of an active material of thepositive electrode 1 b and the layer of an active material of thenegative electrode 2 b. The electrolyte solution is impregnated in thelayer of an active material of the positive electrode 1 b and the layerof an active material of the negative electrode 2 b and finally thesolvent is removed to gelate the electrolyte. The resulting gelatedelectrolyte is impregnated in the active materials to prepare solidelectrolyte layers 1 c, 2 c.

[0038] The positive electrode plate 1 and the negative electrode plate2, this prepared, are housed in the sheathing material for the positiveelectrode 4 and in the sheathing material for the negative electrode 5,respectively. The sheathing material for the positive electrode 4housing the positive electrode plate 1 and the sheathing material forthe negative electrode 5 housing the negative electrode plate 2 arelayered via a separator 3 so that the gelated electrolyte layer 1 c andthe gelated electrolyte layer 2 c will face each other via the separator3. Finally, the outer rim portions of the sheathing material for thepositive electrode 4 and the sheathing material for the negativeelectrode 5 are thermally fused together via hot-melt agent 6 andhermetically sealed together to complete the solid electrolyte cell.

[0039] The separator 3 means a separator-insulator provided between nthe positive and negative electrodes. Any suitable known porous filmsof, for example, polyethylene, polypropylene, polyamide or vinylidenepolyfluoride, used as the separator for the cell, may be used as theseparator 3.

[0040] Although the porous film is used in the above-describedembodiments as the separator, the present invention is not limitedthereto, and a solid electrolyte layer formed on the layer of the activematerial may be used as a separator, as shown in FIG. 2.

[0041] It is noted that the thickness of the solid electrolyte layer isnot less than 1 μm and not more than 300 μm. If the thickness of thesolid electrolyte layer is less than 1 μm, the solid electrolyte layertends to be ruptured under the effect of the electrode surface toproduce internal shorting. If the thickness of the solid electrolytelayer is larger than 300 μm, the solid electrolyte layer tends to beincreased in volume to lower the energy density of the solid electrolytecell. If the thickness of the solid electrolyte layer is not less than 1μm and not more than 300 μm, the positive and negative electrodes can beisolated and insulated from each other more reliably to prevent internalshorting without lowering the energy density of the solid electrolytecell. More preferably, the thickness of the solid electrolyte layer isnot less than 5 μm and not more than 50 μm.

[0042] The thickness of the solid electrolyte layer is the sum of thethickness of the solid electrolyte layer formed on the layer of theactive material for the positive electrode and that of the solidelectrolyte layer formed on the layer of the active material for thenegative electrode, and can be adjusted by adjusting the amount of theelectrolyte solution coated on the active material layers.

[0043] More preferably, the thickness of the solid electrolyte layer isnot less than 5 μm and not more than 50 μm, as described above. Bysetting the thickness of the solid electrolyte layer to not less than 5μm, the internal shorting ratio of the solid electrolyte cell as aproduct can be suppressed to not more than 10%. On the other hand, bysetting the thickness of the solid electrolyte layer to not more than 50μm, it is possible to assure a volumetric energy density of not lessthan 300 Wh/l.

[0044] There is no limitation to the shape of the solid electrolyte cellof the present invention since it may be designed to be cylindrical,angular, coin-shaped or button-shaped, while it may be of any suitabledifferent sizes, such as a thin size or a large size.

EXAMPLES

[0045] A flat-type gelated electrolyte cell, having the above structure,was prepared.

Example 1

[0046] A positive electrode was prepared as follows:

[0047] First, lithium carbonate and cobalt carbonate were mixed at aratio of 0.5 mol to 1 mol, and the resulting mixture was fired in air at900° C. for five hours to produce LiCoO₂ as an active material for thepositive electrode.

[0048] 91 parts by weight of LiCoO₂, thus obtained, 6 parts by weight ofan electrically conductive agent and 10 parts by weight of the binderwere mixed to prepare a positive electrode mixture. As the electricallyconductive agent and as the binder, graphite and a copolymer ofvinylidene fluoride and hexafluoro propylene were used, respectively.

[0049] Finally, the positive electrode mixture was dispersed inN-methyl-2-pyrrolidone to give a slurry which then was coated uniformlyon a surface of an aluminum foil 20 μm thick serving as a positiveelectrode collector and was dried in situ to form a layer of an activematerial of the positive electrode. The resulting product wascompression-molded in a roll press to prepare a positive electrode.

[0050] A negative electrode was prepared as follows:

[0051] First, 42.5 parts by weight of ethylene carbonate, 42.5 parts byweight of propylene carbonate and 15 parts by weight of LiPF₆ were mixedtogether to prepare a plasticizer.

[0052] Then, 30 parts by weight of the above plasticizer, 10 parts byweight of a copolymer of vinylidene fluoride and hexafluoropropylene and60 parts by weight of tetrahydrofuran were mixed together to prepare agelated electrolyte solution.

[0053] On the layer of an active material of the positive electrode andthe layer of an active material of the negative electrode was evenlycoated the above gelated electrolyte solution. The resulting assemblywas allowed to stand at room temperature for eight hours to allow thegelated electrolyte solution to be impregnated in the layer of theactive material of the positive electrode and the layer of the activematerial of the negative electrode. Finally, tetrahydrofuran, as asolvent of the solution of the gelated electrolyte, was vaporized off toform the layer of the gelated electrolyte on the layers of the activematerials of the positive and negative electrodes.

[0054] The negative electrode impregnated with the gelated electrolyteand the positive electrode impregnated with the gelated electrolyte wereplaced face-to-face and pressure bonded together on the gelatedelectrolyte sides thereof to produce a flat-plate gelated electrolytecell having an area of 2.5 cm by 4.0 cm and a thickness of 0.3 mm.

Example 2

[0055] A gelated electrolyte cell was prepared in the same way as inExample 1 except using a copolymer of vinylidene fluoride andhexafluoropropylene and polyvinyl fluoride as a positive electrodebinder and as a negative electrode binder, respectively.

Example 3

[0056] A gelated electrolyte cell was prepared in the same way as inExample 1 except using polyvinylidene fluoride and a copolymer ofvinylidene fluoride and hexafluoropropylene and as a positive electrodebinder and as a negative electrode binder, respectively.

Example 4

[0057] A gelated electrolyte cell was prepared in the same way as inExample 1 except using polyvinylidene fluoride as the binders for thepositive and negative electrodes, respectively.

[0058] In the following Examples 5 and 6, a gelated electrolyte wasimpregnated in the layer of the active material of one of theelectrodes, while a gelated electrolyte was previously added to theelectrode mixture of the other electrode.

Example 5

[0059] A positive electrode was prepared as follows:

[0060] First, lithium carbonate and cobalt carbonate were mixed togetherat a ratio of 0.5 mol to 1 mol and fired in air at 900° C. for fivehours to prepare LiCoO₂ as an active material for the positiveelectrode.

[0061] 42.5 parts by weight of ethylene carbonate, 42.5 parts by weightof propylene carbonate and 15 parts by weight of LiPF₆ were mixedtogether to prepare a plasticizer.

[0062] 83 parts by weight of LiCoO₂, 6 parts by weight of theelectrically conductive agent, 3 parts by weight of a binder and 8 partsby weight of the plasticizer were mixed together and dispersed intetrahydrofuran to give a slurry. As the electrically conductive agentand as the binder, graphite and polyvinylidene fluoride were used,respectively.

[0063] This slurry was uniformly coated on a surface of a strip-shapedaluminum foil 20 μm thick operating as a positive electrode collectorand dried in situ to form a layer of an active material of the positiveelectrode. The resulting product was compression-molded by a roll pressto prepare a positive electrode.

[0064] A negative electrode was prepared as follows:

[0065] First, 90 parts by weight of pulverized graphite powders and 10parts by weight of a binder were mixed together to prepare a negativeelectrode mixture. As the binder, a copolymer of vinylidene fluoride andhexafluoropropylene was used. The binder was dispersed inN-methyl-2-pyrrolidone to form a slurry, which was uniformly coated on asurface of a strip-shaped copper foil 10 μm thick operating as anegative electrode collector and was dried in situ to form a layer of anactive material of the negative electrode. The resulting product wascompression-molded in a roll press to prepare a negative electrode.

[0066] A gelated electrode solution was prepared as follows:

[0067] First, 42.5 parts by weight of ethylene carbonate, 42.5 parts byweight of propylene carbonate and 15 parts by weight of LiPF₆ were mixedtogether to prepare a plasticizer.

[0068] Then, 30 parts by weight of the above plasticizer, 10 parts byweight of a copolymer of vinylidene fluoride and hexafluoropropylene and60 parts by weight of tetrahydrofuran were mixed together to prepare agelated electrolyte solution.

[0069] On the layer of an active material of the negative electrode wasevenly coated the above gelated electrolyte solution. The resultingassembly was allowed to stand at room temperature for eight hours toallow the gelated electrolyte solution to be impregnated in the layer ofan active material of the negative electrode. Finally, tetrahydrofuran,as a solvent of the solution of the gelated electrolyte, was vaporizedoff to form a layer of the gelated electrolyte on the layer of thenegative electrode.

[0070] The negative electrode impregnated with the gelated electrolyteand the positive electrode were placed face-to-face and pressure bondedtogether to produce a flat-plate gelated electrolyte cell having an areaof 2.5 cm by 4.0 cm and a thickness of 0.3 mm.

Example 6

[0071] A positive electrode was prepared as follows:

[0072] First, lithium carbonate and cobalt carbonate were mixed togetherat a ratio of 0.5 mol to 1 mol and fired in air at 900° C. for fivehours to prepare LiCoO2 as an active material for the positiveelectrode.

[0073] 91 parts by weight of LiCoO2, 6 parts by weight of theelectrically conductive agent and 10 parts by weight of the binder weremixed together to prepare a positive electrode mixture. As theelectrically conductive agent and as the binder, graphite andpolyvinylidene fluoride were used, respectively.

[0074] Finally, the positive electrode mixture was dispersed inN-methyl-2-pyrrolidone to give a slurry which was then coated uniformlyon a sole side of an aluminum foil 20 μm thick operating as a positiveelectrode collector and was dried in situ to form a layer of a positiveelectrode active material. The resulting product was compression-moldedby a roll press to prepare a positive electrode.

[0075] A negative electrode was prepared as follows:

[0076] First, 42.5 parts by weight of ethylene carbonate, 42.5 parts byweight of propylene carbonate and 15 parts by weight of LiPF₆ were mixedtogether to prepare a plasticizer.

[0077] Then, 65 parts by weight of pulverized graphite, 10 parts byweight of polyvinylidene fluoride, as a binder, and 25 parts by weightof the above plasticizer, were mixed together and dispersed intetrahydrofuran to prepare a slurry.

[0078] Finally, this slurry was coated evenly on one surface of astrip-shaped copper foil, 10 μm thick, operating as a negative electrodecollector, an was dried in situ to form a layer of an active material ofthe negative electrode. The resulting product was compression-molded ona roll press to prepare a negative electrode.

[0079] A gelated electrode solution was prepared as follows:

[0080] First, 42.5 parts by weight of ethylene carbonate, 42.5 parts byweight of propylene carbonate and 15 parts by weight of LiPF6 were mixedtogether to prepare a plasticizer.

[0081] Then, 30 parts by weight of the above plasticizer, 10 parts byweight of a copolymer of vinylidene fluoride and hexafluoropropylene and60 parts by weight of tetrahydrofuran were mixed together to prepare agelated electrolyte solution.

[0082] On the layer of an active material of the positive electrode wasevenly coated the above gelated electrolyte solution. The resultingassembly was allowed to stand at room temperature for eight hours toallow the gelated electrolyte solution to be impregnated in the layer ofan active material of the positive electrode. Finally, tetrahydrofuran,as a solvent of the solution of the gelated electrolyte, was vaporizedoff to form the layer of the gelated electrolyte on the layers of theactive material of the positive electrode.

[0083] The negative electrode impregnated with the gelated electrolyteand the positive electrode impregnated with the gelated electrolyte wereplaced face-to-face and pressure bonded together to produce a flat-plategelated electrolyte cell having an area of 2.5 cm by 4.0 cm and athickness of 0.3 mm.

Example 7

[0084] A gelated electrolyte cell was prepared in the same way as inExample 1 except arraying a porous film of polyethylene as a separatorbetween the positive and negative electrodes.

[0085] In the Comparative Example 1, shown below, a gelated electrodewas sandwiched between the layer of an active material of the positiveelectrode and a layer of an active material of the negative electrode,to prepare a cell, without impregnating the layer of the active materialwith the gelated electrolyte. In the Comparative Example 2, a gelatedelectrolyte was previously mixed into the electrode mixture. In theComparative Example 3, the gelated electrolyte was sandwiched betweenthe layer of an active material of the positive electrode and a layer ofan active material of the negative electrode, to prepare a cell, whilsta gelated electrolyte was previously mixed into the electrode mixture.

Comparative Example 1

[0086] A positive electrode was prepared as follows:

[0087] First, lithium carbonate and cobalt carbonate were mixed togetherat a ratio of 0.5 mol to 1 mol and fired in air at 900° C. for fivehours to prepare LiCoO₂ as an active material for the positiveelectrode.

[0088] 91 parts by weight of LiCoO₂, 6 parts by weight of theelectrically conductive agent and 10 parts by weight of the binder weremixed together to prepare a positive electrode mixture. As theelectrically conductive agent and as the binder, graphite and acopolymer of polyvinylidene fluoride and hexafluoropropylene were used,respectively.

[0089] Finally, the positive electrode mixture was dispersed inN-methyl-2-pyrrolidone to give a slurry which was then coated uniformlyon a sole side of an aluminum foil 20 μm thick operating as a positiveelectrode collector and was dried in situ. The resulting product wascompression-molded by a roll press to prepare a positive electrode.

[0090] A negative electrode was prepared as follows:

[0091] First, 90 parts by weight of pulverized graphite powders and 10parts by weight of a binder were mixed to prepare a negative electrodemixture. As a binder, a copolymer of vinylidene fluoride andhexafluoropropylene was used. The binder was dispersed inN-methyl-2-pyrrolidone to form a slurry. This slurry was evenly coatedon a sole surface of a strip-shaped copper foil, 10 μm thick, operatingas a negative electrode collector, and was dried in situ to form a layerof an active material of the negative electrode, which was thencompression-molded to form a negative electrode.

[0092] A gelated electrolyte was produced as follows:

[0093] First, 42.5 parts by weight of ethylene carbonate, 42.5 parts byweight of propylene carbonate and 15 parts by weight of LiPF₆ were mixedtogether to prepare a plasticizer.

[0094] To 30 parts by weight of the plasticizer were mixed 10 parts byweight of a copolymer of vinylidene fluoride and hexafluoropropylene and60 parts by weight of tetrahydrofuran and dissolved to prepare a gelatedelectrolyte.

[0095] The gelated electrolyte was coated on a Teflon sheet to give afilm of a gelated electrolyte which was sandwiched between a layer of anactive material of the positive electrode and a layer of an activematerial of the negative electrode and pressure bonded together toprepare a flat-plate gelated electrolyte cell having an area of 2.5 cmby 4.0 cm and a thickness of 0.3 mm.

Comparative Example 2

[0096] A positive electrode was prepared as follows:

[0097] First, lithium carbonate and cobalt carbonate were mixed at aratio of 0.5 mol to 1 mol, and the resulting mixture was fired in air at900° C. for five hours to produce LiCoO₂ as an active material for thepositive electrode.

[0098] 42.5 parts by weight of ethylene carbonate, 42.5 parts by weightof propylene carbonate and 15 parts by weight of LiPF₆ were mixedtogether to prepare a plasticizer.

[0099] 83 parts by weight of LiCoO₂, 6 parts by weight of theelectrically conductive agent, 3 parts by weight of the binder and 8parts by weight of the plasticizer were mixed together and dispersed intetrahydrofuran to give a slurry. As the electrically conductive agentand as the binder, graphite and polyvinylidene fluoride were used,respectively.

[0100] Finally, this slurry was uniformly coated on a surface of astrip-shaped aluminum foil 20 μm thick, operating as a positiveelectrode collector, and was dried in situ to form a layer of an activematerial of the positive electrode. The resulting product wascompression-molded by a roll press to prepare a positive electrode.

[0101] A negative electrode was prepared as follows:

[0102] 42.5 parts by weight of ethylene carbonate, 42.5 parts by weightof propylene carbonate and 15 parts by weight of LiPF₆ were mixedtogether to prepare a plasticizer.

[0103] Then, 65 parts by weight of pulverized graphite powders, 10 partsby weight of polyvinylidene fluoride, as a binder, and 25 parts byweight of the plasticizer, were mixed together and dispersed intetrahydrofuran to prepare a slurry.

[0104] Finally, this slurry was uniformly coated on a surface of astrip-shaped copper foil, 10 μm thick, operating as a positive electrodecollector, and was dried in situ to form a layer of an active materialof the negative electrode. The resulting product was compression-moldedby a roll press to prepare a negative electrode.

[0105] The positive electrode and the negative electrode were placedface-to-face and pressure bonded together to form a flat-plate gelatedelectrolyte cell having an area of 2.5 cm by 4.0 cm and a thickness of0.3 mm.

Comparative Example 3

[0106] A positive electrode was prepared as follows:

[0107] First, lithium carbonate and cobalt carbonate were mixed at aratio of 0.5 mol to 1 mol, and the resulting mixture was fired in air at900° C. for five hours to produce LiCoO₂ as an active material for thepositive electrode.

[0108] 42.5 parts by weight of ethylene carbonate, 42.5 parts by weightof propylene carbonate and 15 parts by weight of LiPF₆ were mixedtogether to prepare a plasticizer.

[0109] 83 parts by weight of LiCoO₂, 6 parts by weight of theelectrically conductive agent, 3 parts by weight of the binder and 8parts by weight of the plasticizer were mixed together and dispersed intetrahydrofuran to give a slurry. As the electrically conductive agentand as the binder, graphite and polyvinylidene fluoride were used,respectively.

[0110] This slurry was uniformly coated on a surface of a strip-shapedaluminum foil 20 μm thick, operating as a positive electrode collector,and was dried in situ to form a layer of an active material of thepositive electrode. The resulting product was compression-molded by aroll press to prepare a positive electrode.

[0111] A negative electrode was prepared as follows:

[0112] 42.5 parts by weight of ethylene carbonate, 42.5 parts by weightof propylene carbonate and 15 parts by weight of LiPF₆ were mixedtogether to prepare a plasticizer.

[0113] Then, 65 parts by weight of pulverized graphite powders, 10 partsby weight of polyvinylidene fluoride, as a binder, and 25 parts byweight of the plasticizer, were mixed together and dispersed intetrahydrofuran to prepare a slurry.

[0114] This slurry was coated evenly on a sole surface of a strip-shapedcopper foil, 10 μm thick, operating as a negative electrode collector,and was dried in situ to prepare a negative electrode.

[0115] A gelated electrolyte was prepared as follows:

[0116] First, 42.5 parts by weight of ethylene carbonate, 42.5 parts byweight of propylene carbonate and 15 parts by weight of LiPF₆ were mixedtogether to prepare a plasticizer.

[0117] To 30 parts by weight of the plasticizer were mixed 10 parts byweight of a copolymer of vinylidene fluoride and hexafluoropropylene and60 parts by weight of tetrahydrofuran and dissolved to prepare a gelatedelectrolyte.

[0118] The gelated electrolyte was coated on a Teflon sheet to give afilm of a gelated electrolyte which was sandwiched between a layer of anactive material of the positive electrode and a layer of an activematerial of the negative electrode to prepare a flat-plate gelatedelectrolyte cell.

Evaluation of Characteristics

[0119] For each cell, prepared as described above, a theoreticalcapacity was found, and time rate discharge was carried out to evaluatethe discharging capacity.

[0120] The evaluation was made under the conditions of room temperatureof 23° C. First, for each cell, an upper limit of the charging voltagewas set to 4.2 V, and the constant current constant voltage charging wascarried out at a charging current of 6 mA. Each charged cell was thendischarged at a constant current until a electrode voltage of 2.5 v wasreached. For discharging, the current was set to 3 mA, 15 mA and to 30mA for the 10-hour rate discharge, 2-hour rate discharge and to 1-hourrate discharge, respectively.

[0121] From the average voltage at the time of discharging, an output ateach time rate discharging was found.

[0122] Table 1 shows a theoretical capacity and a discharge output foreach of the cells of the Examples 1 to 7 and the Comparative Examples 1to 3. theoretical capacity discharging output (mWh) (mAh) 1/C 1/5C 1/2C1C Ex.1 30.0 108.0 107.5 104.4 89.9 Ex.2 30.0 107.9 107.5 104.1 90.1Ex.3 29.8 107.9 106.8 103.6 88.5 Ex.4 29.8 107.2 106.9 103.3 88.2 Ex.529.9 107.1 104.9 100.8 84.1 Ex.6 30.0 107.7 106.7 102.2 85.4 Ex.7 29.9107.6 106.5 103.5 88.8 Comp. Ex.1 30.0 37.4 13.2 3.4 <1.0 Comp. Ex.229.9 106.6 103.3 88.9 70.1 Comp. Ex.3 29.9 106.1 95.4 74.2 43.3

[0123] As may be seen from Table 1, in the Examples 1 to 6 in which thegelated electrolyte was impregnated in at least one of the layers of theactive materials of the two electrodes, the cells having highdischarging outputs and superior load characteristics were obtained.Also, from Example 7, it was seen that a cell having a high dischargingoutput and superior load characteristics could be obtained even in casea separator was arranged between the positive and negative electrodes.

[0124] In the Comparative Example 1 in which the gelated electrode isnot impregnated in the layer of an active material of the electrode andis sandwiched between the layers of the active material, the dischargeoutput was low, whereas, in the Comparative Example 2 in which thegelated electrolyte is previously added to the electrode mixture, asufficient output was not achieved. In the Comparative Example 3 inwhich part of the gelated electrolyte is added to the electrode mixtureand the gelated electrolyte and is sandwiched between the layers of theactive material, the discharge output could not be improved.

[0125] Thus, it has been found that, by applying the solution of thegelated electrolyte on the layer of an active material of the electrodeand by impregnating the gelated electrolyte in the layer of an activematerial of the electrode, a cell can be obtained which has superiorcontact properties between the active material and the electrolyte and ahigh discharge output.

What is claimed is:
 1. A solid electrolyte cell comprising: an electrodehaving a current collector and a layer of an active material formed onsaid current collector and containing an active material and a binder; asolid electrolyte layer being formed by impregnating a solid electrolytedissolved in a solvent on said layer of the active material.
 2. Thesolid electrolyte cell according to claim 1 wherein said solidelectrolyte contains a high-molecular matrix material and is in agelated state.
 3. The solid electrolyte cell according to claim 2wherein the high-molecular matrix material and the binder in said layerof the active material are the same compound.
 4. The solid electrolytecell according to claim 3 wherein the high-molecular matrix material andthe binder are a fluorine-based high-molecular material.
 5. The solidelectrolyte cell according to claim 4 wherein the fluorine-basedhigh-molecular material is polyvinylidene fluoride.
 6. The solidelectrolyte cell according to claim 4 wherein the fluorine-basedhigh-molecular material is a copolymer of vinylidene fluoride andhexafluoropropylene.
 7. The solid electrolyte cell according to claim 1wherein the negative electrode contains a material capable ofdoping/undoping lithium.
 8. The solid electrolyte cell according toclaim 7 wherein the material capable of doping/undoping lithium is acarbon material.
 9. The solid electrolyte cell according to claim 1wherein the positive electrode contains a compound oxide of lithium anda transition metal.
 10. The solid electrolyte cell according to claim 1wherein said solid electrolyte layer is formed on each of a layer of anactive material of a positive electrode and a layer of an activematerial of a negative electrode, with the solid electrolyte layersbeing in contact with each other.
 11. The solid electrolyte cellaccording to claim 1 wherein said solid electrolyte layer is formed oneach of a layer of an active material of a positive electrode and alayer of an active material of a negative electrode, with the solidelectrolyte layers facing each other with a separator in-between.
 12. Amethod for manufacturing a solid electrolyte cell comprising the stepsof: applying a paint containing an active material and a binder to acurrent collector to form a layer of an active material; andimpregnating a solid electrolyte in said layer of the active materialformed by said active material layer forming step; said impregnatingstep including applying the paint comprised of said solid electrolytedissolved in a solvent on the layer of the active material to allow thepaint to be permeated into the layer of the active material andsubsequently drying the solvent.
 13. The method according to claim 12wherein said solid electrolyte contains a high-molecular matrix materialand wherein said high-molecular matrix material and the binder are thesame compound,
 14. The method according to claim 13 wherein saidhigh-molecular matrix material and the binder are fluorine-basedhigh-molecular material.
 15. The method according to claim 14 whereinsaid fluorine-based high-molecular material is polyvinylidene fluoride.16. The method according to claim 14 wherein said fluorine-basedhigh-molecular material is a copolymer of vinylidene fluoride andhexafluoropropylene.